1. Field of the Invention
The present invention relates to a method and apparatus for admixing concentrated photographic compositions with liquids to form processing solutions, and more specifically for admixing shear-thinable, processing compositions having the consistency of a stiff paste. As used herein the term "photographic processing solution" is intended to include developing solutions, replenisher solutions, starter solutions, and other working photographic solutions.
2. Brief Description of the Prior Art
It is well known to supply photographic processing compositions in concentrated form, including liquids, powders, tablets and even pastes and gels, which are diluted with water to form photographic processing solutions.
Due perhaps to the simplicity of the dispensing and mixing equipment, liquid concentrates are generally preferred over the other forms of concentrates by most professional photofinishers. In one approach, for example, the liquids are supplied in plastic bottles that are closed by a rupturable membrane and a protective cap. After removing the cap, each bottle is positioned upside-down over a receiving tank where a sharp probe pierces the membrane and releases the liquid. Water is added to dilute the mixture to the proper concentration for a photographic processing solution.
Although liquid concentrates have been widely accepted, powders have certain advantages, particularly in connection with storage and shipping. Amateur photographers, for example, often prefer the powders for their compact form and long shelf life. In general, however, many of the powdered concentrates are considered difficult to dissolve and dilute. While satisfactory equipment is certainly available for this purpose, it tends to be either bulky or suitable only for small batches, and is not particularly convenient for use by unskilled operators or with high volume automated processing equipment.
Of course some of the problems associated with powders can be alleviated by compressing them into tablets. Generally speaking, however, the tablets are not a viable commercial alternative. In particular, the tablets cannot incorporate liquids, and many photographic processing compositions are not amenable to tablet formation. Those that are, usually incorporate binding agents which can make dissolution of the tablet quite difficult and/or cause undesirable sensitometric effects in processing. Although effervescing agents have been employed to promote prompt dissolution, they are generally not very effective and introduce additional costs and complexity in the manufacturing operation.
At least several attempts have been made to obtain the advantages simultaneously of the powders and the liquids by constructing pastes and gels which contain relatively little water but are easier to dissolve than their corresponding powders. Examples of this approach are described in U.S. Pat. No. 2,735,774, entitled CONCENTRATED PHOTOGRAPHIC FIXING SOLUTIONS, issued in the name of R. W. Henn in 1956; British Patent No. 4689 AD 1894, entitled IMPROVEMENTS IN THE PREPARATION, PACKING AND STORING OF PHOTOGRAPHIC CHEMICAL COMPOUNDS issued in the name of the J. R. Gale et al in 1895; and Italian Patent No. 427,967, entitled METHOD FOR THE PREPARATION OF A DEVELOPER CONDENSED INTO PASTE, FOR PLATES, PHOTOSENSITIVE PAPER FILMS, issued in the name of V. Barra.
Although pastes and gels have been known for some time, their advantages have not been fully realized, nor has the prior art recognized how to use the pastes to obtain the full benefit of these advantages. By way of example only, it appears that pastes have been dispensed manually from their supply containers and mixed by manual stirring and similar techniques. For this and other reasons most pastes were relatively soft, and contained an undesirable amount of water. Pastes having reduced amounts of water were considered difficult to dissolve and possessed some of the disadvantages of tablets. It will become apparent from the following description that the present invention overcomes many of these disadvantages of the prior art and provides significant additional features not previously available.